1. Field of the Invention
The present invention relates to a magnetic head and a magnetic storage apparatus for perpendicular magnetic recording.
2. Description of Related Art
There has been an increasing demand for larger capacity and smaller size on the hard disc drive used as external storage for information processing apparatus such as computers. This demand has been met mainly by increasing the recording density of a hard disc. The disadvantage of increasing the recording density in conventional longitudinal recording is that it is necessary to reduce the thickness of the recording layer because the demagnetizing field reaches a maximum in the written magnetization transition region on the recording medium. The result is that recorded data disappear due to thermal scattering. By contrast, it is comparatively easy to increase the recording density for perpendicular recording (in which magnetization for recording takes place in the thickness direction of the recording medium) because the demagnetizing field reaches a minimum in the written magnetization transition region and this alleviates the necessity of reducing the thickness of the recording medium.
Recording signals on a perpendicular recording medium with a magnetic head for perpendicular recoding involves conversion by a coil of electric signals into magnetic signals, which produce a magnetic flux in the secondary magnetic pole and the recording magnetic pole. The magnetic flux passes through the secondary magnetic pole and the recording magnetic pole and penetrates the perpendicular recording layer. The magnetic flux further passes through the soft magnetic underlayer (below the perpendicular recording layer) and returns to the secondary magnetic pole, thereby forming a closed loop. The secondary magnetic pole serves to return the magnetic field (which has occurred in the perpendicular recording layer and the soft magnetic underlayer) from the recording pole to the recording pole again in a magnetically effective way. The flow of a magnetic flux in this way performs signal recording in terms of magnetization on a perpendicular recording medium.
The magnetic head used for conventional longitudinal recording requires that the upper magnetic core and the lower magnetic core should be as close to each other as possible, with a recording gap interposed between them. For a narrow track to be formed on the step containing the coil etc., it is necessary to form the tip and the yoke separately (separate structure), as mentioned in JP-A No. 276707/2000. This is not the case for the magnetic head for perpendicular magnetic recording, which does not necessarily need the separate structure because the main magnetic pole can be formed on a flat surface.
An increase in recording density entails a reduction in track width, and these results in a decrease in the magnetic field generated by the magnetic pole. This in turn makes it necessary to form the recording magnetic pole from a material having a high saturation magnetic flux density. However, because of its large magnetostriction, such a material is not favorable to the conventional main magnetic pole elongating in the depthwise direction from the flying surface. Such a magnetic pole causes magnetization to orient in the direction of the flying surface even when no current is flowing through the coil. (This phenomenon is called remanent magnetization.) The magnetic head with remanent magnetization causes so-called “erasure after recording”, which is a phenomenon that signals written on a recording medium are erased while the head is not performing recording.